Aqueous cleaning processes are a mainstay of conventional domestic and industrial textile fabric cleaning methods. On the assumption that the desired level of cleaning is achieved, the efficacy of such conventional processes is usually characterised by their levels of consumption of energy, water and detergent. In general, the lower the consumption requirements with regard to these three components, the more efficient the washing process is deemed. The downstream effect of reduced water and detergent consumption can also be significant, as this minimises the need for disposal of aqueous effluent, which is both extremely costly and detrimental to the environment.
Such washing processes involve aqueous submersion of fabrics followed by soil removal, aqueous soil suspension, and water rinsing. In general, within practical limits, the higher the level of energy (or temperature), water and detergent which is used, the better the cleaning. One key issue, however, concerns water consumption, as this sets the energy requirements (in order to heat the wash water), and the detergent dosage (to achieve the desired detergent concentration). In addition, the water usage level defines the mechanical action of the process on the fabric, which is another important performance parameter; this is the agitation of the cloth surface during washing, which plays a key role in releasing embedded soil. In aqueous processes, such mechanical action is provided by the water usage level in combination with the drum design for any particular washing machine. In general terms, it is found that the higher the water level in the drum, the better the mechanical action. Hence, there is a dichotomy created by the desire to improve overall process efficiency (i.e. reduce energy, water and detergent consumption), and the need for efficient mechanical action in the wash.
Various different approaches to the development of new cleaning technologies have been reported in the prior art, including methods which rely on electrolytic cleaning or plasma cleaning, in addition to approaches which are based on ozone technology, ultrasonic technology or steam technology. Thus, for example, WO2009/021919 teaches a fabric cleaning and disinfection process which utilises UV-produced ozone along with plasma. An alternative technology involves cold water washing in the presence of specified enzymes, whilst a further approach which is particularly favoured relies on air-wash technology and, for example, is disclosed in US2009/0090138. In addition, various carbon dioxide cleaning technologies have been developed, such as the methods using ester additives and dense phase gas treatments which are described in U.S. Pat. No. 7,481,893 and US2008/0223406, although such methods generally find greater applicability in the field of dry cleaning. Many of these technologies are, however, technically very complex.
In the light of the challenges which are associated with aqueous washing processes, the present applicants have previously devised a new approach to the problem that allows the deficiencies demonstrated by the methods of the prior art to be mitigated or overcome. The method which is provided eliminates the requirement for the use of large volumes of water, but is still capable of providing an efficient means of cleaning and stain removal, whilst also yielding economic and environmental benefits.
Thus, in WO2007/128962 there is disclosed a method and formulation for cleaning a soiled substrate, the method comprising the treatment of the moistened substrate with a formulation comprising a multiplicity of polymeric particles, wherein the formulation is free of organic solvents. The substrate may be wetted so as to achieve a substrate to water ratio of between 1:0.1 to 1:5 w/w, and optionally, the formulation additionally comprises at least one cleaning material, which typically comprises a surfactant, which most preferably has detergent properties. The substrate may comprise a textile fibre. The polymeric particles may, for example, comprise particles of polyamides, polyesters, polyalkenes, polyurethanes or their copolymers, a particular example being nylon beads.
The use of this cleaning method, however, presents a requirement for the nylon beads to be efficiently separated from the cleaned substrate at the conclusion of the cleaning operation, and this issue was initially addressed in WO2010/094959, which provides a novel design of cleaning apparatus requiring the use of two internal drums capable of independent rotation, and which finds application in both industrial and domestic cleaning processes.
With a view to providing a simpler, more economical means for addressing the problem of efficient separation of the cleaning beads from the substrate at the conclusion of the cleaning process, however, a further apparatus is disclosed in WO2011/064581. The apparatus of WO2011/064581, which finds application in both industrial and domestic cleaning processes, comprises a perforated drum and a removable outer drum skin which is adapted to prevent the ingress or egress of fluids and solid particulate matter from the interior of the drum. The cleaning method requires attachment of the outer skin to the drum during a first wash cycle, after which the skin is removed prior to operating a second wash cycle, following which the cleaned substrate is removed from the drum.
The apparatus and method of WO2011/064581 is found to be extremely effective in successfully cleaning substrates, but the requirement for the attachment and removal of the outer skin detracts from the overall efficiency of the process and the present applicants have, therefore, sought to address this aspect of the cleaning operation and to provide a process wherein this procedural step is no longer necessary. Thus, by providing for continuous circulation of the cleaning beads during the cleaning process, it has been found possible to dispense with the requirement for the provision of an outer skin.
Thus, in WO2011/098815, the present applicants provided an apparatus for use in the cleaning of soiled substrates, the apparatus comprising housing means having a first upper chamber with a rotatably mounted cylindrical cage mounted therein and a second lower chamber located beneath the cylindrical cage, and additionally comprising at least one recirculation means, access means, pumping means and a multiplicity of delivery means, wherein the rotatably mounted cylindrical cage comprises a drum having perforated side walls where up to 60% of the surface area of the side walls comprises perforations comprising holes having a diameter of no greater than 25.0 mm.
Although the apparatus disclosed in WO2010/094959, WO2011/064581 and particularly WO2011/098815 provided considerable improvements there remain several drawbacks associated with using an apparatus of this nature for the cleaning of soiled substrates with formulations comprising solid particulate cleaning material and wash water. In particular, the use of solid particulate material in such apparatus provides challenges associated with the transport of the solid particulate material throughout the cleaning process and storage of the material prior to commencing the cleaning operation and after its completion. Typically, the cleaning apparatus must therefore be adapted to accommodate both the storage of solid particulate material therein and to facilitate its transport so that it can be agitated with soiled substrates contained within a cleaning volume and separated from the washload at the end of the wash cycle. In order to accommodate effective agitation of the solid particulate material with soiled substrates and, ultimately, its separation from the washload, it is desirable to maximise the cleaning volume. Generally this aim cannot easily be attained without increasing the overall size or footprint of the apparatus.
The present invention seeks to provide a cleaning apparatus for use in the cleaning of soiled substrates with a solid particulate material that can ameliorate or overcome the above-noted problems associated with the prior art. Particularly, there is desired an apparatus and method for the cleaning of soiled substrates with a solid particulate cleaning material which can provide an enhanced cleaning capacity relative to the footprint of the apparatus. Further desired is an apparatus which can achieve good cleaning efficiency with a specific footprint size whilst further reducing the requirements for energy, water and detergents per unit quantity (e.g. weight) of soiled substrate washed. Further desired is an apparatus which improves the separation of said solid particulate material from the substrate after cleaning.